code review 154540044: cmd/gc: emit code for extern = <N>

cmd/gc: emit code for extern = <N>

https://codereview.appspot.com/152700045/ made it possible for struct literals assigned to globals to use <N> as the RHS. Normally, this is to zero out variables on first use. Because globals are already zero (or their linker initialized value), we just ignored this.

Now that <N> can occur from non-initialization code, we need to emit this code. We don't use <N> for initialization of globals any more, so this shouldn't cause any excessive zeroing.

Fixes issue 8961.

[DMorsing, 2014-10-20 12:44:10]

Hello golang-codereviews@googlegroups.com (cc: bradfitz@golang.org,
rsc@golang.org),

I'd like you to review this change to
https://code.google.com/p/go/

[rsc, 2014-10-20 14:47:53]

LGTM

[DMorsing, 2014-10-20 14:59:16]

*** Submitted as https://code.google.com/p/go/source/detail?r=98477b56eb36 ***

cmd/gc: emit code for extern = <N>

https://codereview.appspot.com/152700045/ made it possible for struct literals
assigned to globals to use <N> as the RHS. Normally, this is to zero out
variables on first use. Because globals are already zero (or their linker
initialized value), we just ignored this.

Now that <N> can occur from non-initialization code, we need to emit this code.
We don't use <N> for initialization of globals any more, so this shouldn't cause
any excessive zeroing.

Fixes issue 8961.

LGTM=rsc
R=golang-codereviews, rsc
CC=bradfitz, golang-codereviews
https://codereview.appspot.com/154540044